Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method whereby a terminal transmits an acknowledgement/not-acknowledgement (ACK/NACK) with serving cells aggregated using different types of radio frames, and a device thereof.
Related Art
Long Term Evolution (LTE) based on 3rd Generation Partnership Project (3GPP) Technical Specification (TS) Release 8 is the leading next-generation mobile communication standard.
As disclosed in 3GPP TS 36.211 V8.7.0 (2009-05) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, in LTE, a physical channel can be divided into a Physical Downlink Shared Channel (PDSCH) and a Physical Downlink Control Channel (PDCCH), that is, downlink channels, and a Physical Uplink Shared Channel (PUSCH) and a Physical Uplink Control Channel (PUCCH), that is, uplink channels.
A PUCCH is an uplink control channel used to send uplink control information, such as a Hybrid Automatic Repeat reQuest (HARQ), an acknowledgement/not-acknowledgement (ACK/NACK) signal, a Channel Quality Indicator (CQI), and a Scheduling Request (SR).
Meanwhile, 3GPP LTE-Advanced (LTE-A) as an evolved version of 3GPP LTE is progressing. A technique introduced in the 3GPP LTE-A includes a carrier aggregation.
The carrier aggregation uses a plurality of component carriers. The component carrier is defined by a center frequency and a bandwidth. One downlink component carrier or a pair of an uplink component carrier and the downlink component carrier corresponds to one cell. A terminal receiving a service using a plurality of downlink component carriers may receive a service from a plurality of serving cells. The carrier aggregation include a cross carrier scheduling where a scheduling cell is different from a scheduled cell and a non-cross carrier scheduling where the scheduling cell is the same as the scheduled cell.
Meanwhile, serving cells using different radio frame structures such as a serving cell using a time division duplex (TDD) radio frame and a serving cell using a frequency division duplex (FDD) radio frame may be aggregated in a next generation wireless communication system. That is, a plurality of serving cells using different types of radio frames may be allocated to the terminal. Alternatively, even if a plurality of serving cells using the same type of radio frame is aggregated, uplink-downlink (UL-DL) configurations of respective serving cells may be different from each other.
For example, a TDD cell using a TTD frame may be configured as a primary cell for the terminal. A FDD cell using a FDD frame may be configured as a primary cell for the terminal. In this case, when the terminal receives data by a downlink subframe of the FDD cell, which uplink subframe of the TDD cell transmits an ACK/NACK for the data may cause a problem. For example, although a time point to transmit the ACK/NACK is determined by an ACK/NACK timing, the above method may not be applied to a partial downlink subframe of the FDD cell.
The uplink subframes may not be continuously configured in the TDD frame of the TDD cell. That is, the downlink subframe coexists with the uplink subframe in different times. On the contrary, in the FDD frame of the FDD cell, a downlink subframe and an uplink subframe may be continuously configured in different frequency bands. Accordingly, if data are received by a downlink subframe of the FDD frame existing at the same time as that of the uplink subframe of the TDD frame, when transmits an ACK/NACK for the data may cause a problem.